my $login_tot;
my $campaign_tot;
my $work_tot;
foreach my $func ('login','campaign','work') {
    # do some things
    my $tmp = calc_difference($var1, $var2);
    # update _tot vars here
}

##</code><code>##

${$func . "_tot"} += $tmp;

##</code><code>##

my $ref = "$func" . "_tot";
$$ref++;